Abstract

Lactic acid bacteria (LAB) are a diverse group of Gram-positive microbes that ferment carbohydrates to organic acids, primarily lactic acid. LAB include organisms vitally important to the production of foods, bread, and wine, and they include major human pathogens for diseases of the oropharyneal space, lungs, mouth, and skin. For all of these organs, the production of lactic acid rapidly and substantially lowers the pH of their external environments. Because bacterial membranes are essentially porous to protons, these bacteria are at risk of damaging cellular constituents to the extent that growth ceases, and eventually they do not survive. Thus, the LAB have evolved a broad range of mechanisms to protect themselves from acidification, to repair cellular damage, and to use low-pH environments to outcompete other bacteria. In this chapter, we describe the acid-stress-responsive mechanisms of representative LAB, which have provided a framework of how these organisms respond to, and prosper in, acidic environments.

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